When designing integrated circuits and printed circuit boards where the circuitry is to drive at least one indicator lamp or LED as a display or indicator device, problems can arise when the printed circuit board has the LEDs inserted into it. Because the LED is a two terminal device, it can easily be placed into the board in the wrong orientation. This results in an indicator device which cannot be turned on. The possibility of this error being made is high, because the LED device is a simple device with a wire at each end, and it is difficult to tell from a quick visual inspection which end is which, that is the cathode and anode terminals appear the same. When automatic equipment is used, the LED devices may be loaded into an automated pick and place device incorrectly, so that although the machine places all of the LEDs in the same manner, the operator can still cause errors to occur.
The boards produced with the LEDs must be tested against the possibility that this placement error has occurred. Any boards which are produced with incorrectly placed LEDs must be reworked. This results in a lower initial yield and additional time and cost per unit, as these units must first be sent to a rework station and then subjected to a second round of testing before being qualified for shipment.
A need for a circuit and method which will eliminate rework for incorrectly placed LEDs in circuit boards thus exists.